Potentiometers



T. LOCK POTENTIOMETERS Dec. 12, 1961 2 Sheets-Sheet 1 Filed April 4, 1960 [NVEn/To r; TOM LOC K Af't'OFHQJ/ S Wow-a Bali/M T. LOCK POTENTIOMETERS Dec. 12, 1961 2 Sheets-Sheet 2 Filed April 4, 1960 m T W V w TOM LOCK fHTormzys Uitc States Patent Ofiicc 3,013,238 Patented Dec. 12, 1961 3,013,238 POTENTIOMETERS Tom Lock, Northampton, England, assignor to Associated Electrical Industries Limited, London, England, a British company Filed Apr. 4, 1960, Ser. No. 19,779 Claims priority, application Great Britain Apr. 6, 1959 7 Claims. (Cl. 338-180) This invention relates to otentiometers.

According to the present invention a potentiometer comprises a resistance member of generally cylindrical shape, an annular rotatable member surrounding the resistance member and having an internal screw thread in which there lies a contact member which registers against the resistance member, and means for preventing rotation of said contact member about said resistance member whereby rotation of the rotatable member causes movement of the contact member axially of the resistance member, an electrical connection from said contact member to a fixed terminal, and at least one further terminal connected to the resistance member.

In order that the invention may be more fully understood reference will now be made to the accompanying drawings.

FIG. 1 shows a sectional elevation of a potentiometer embodying the invention in one form;

FIG. 2 is a sectional plan along the line II-II of FIG. 1;

FIG. 3 shows a sectional elevation of a potentiometer embodying the invention in an alternative form; and

FIG. 4 is a sectional plan along the line IV-IV of FIG. 3.

Referring to FIG. 1 and FIG. 2 a resistance member 1 is formed by a core 21 of generally cylindrical shape secured to an insulating base 5. Core is non-symmetrical in that it has two flattened portions 2 and 3 extending along opposite sides thereof. These flattened portions are shown more clearly in FIG. 2. A resistance wire 4 is wound in helical fashion around the core 21 and one end of wire 4 is connected to an external terminal 6 extending through the base 5 of the potentiometer while the other end of wire 4 is connected to a conductor wire extending axially through the centre of core 1 and base 5 and forming a further terminal 7. Thus if a potential difference is applied between terminals 6 and 7 a potential gradient will be established along the length of the resistance member 1.

An annular metallic cylinder 8 which is preferably of stainless steel surrounds member 1 and is rotatable relative thereto by means of an insulating extension member 9 secured to one end of member 8 and having a screw head. Member 8 is provided with an internal screw thread extending the length of core 1. A contact member in the form of an arcuate spring 10 lies in this screw thread and is provided with two integral contact fingers 11 and 12 at either end thereof. These contact fingers respectively contact the flattened portions 2 and 3 of the core 1 and thus make electrical connection with the portion of the helical wire 4 at the points of contact. On rotation of member 8 by means of the screw head on member 9 it will be seen that spring 10 will be prevented from rotation by the force exerted by flattened portions 2 and 3 against contact fingers 11 and 12. Thus as member 8 is rotated spring 10 progresses axially relative to the core. The potential of spring 10 and hence of member 8 is variable in accordance with the rotation of member 9. A terminal 13 is secured to base 5 and is connected by means of a wiping contact 14 to the bottom of member 8. Thus the potential at terminals 13 can be varied between the potentials of terminals 6 and 7 at will.

An insulating housing 15 surrounds member 8 and is secured to base 5. Member 9 is rotatably supported within this housing by means of a circlip 16. If desired a further metal screen can be placed around housing 15 for additional protection.

An advantage of the above arrangement is that the potentiometer cannot be over-run at either end since when spring 10 reaches the end cap 17 provided on core 21 any further rotation of member 9 will merely cause spring 10 to jump the threads in which it lies without any damage being caused. A similar jumping action will take place if member 9 is rotated when spring 10 is at the base end of resistance member 1.

If required the potentiometer can be assembled as a sealed unit, in which case a sealed rotating joint is provided between the inner surface of housing 15 and the outer surface of member 9.

In the alternative embodiment illustrated in FIG. 3 and FIG. 4 a resistance member 31 is formed by a core 32 of cylindrical shape secured to an insulating base 33 and having a resistance wire 34 wound in helical fashion around core 32, one end of wire 34 being connected to an external terminal 35 extending through base 33 of the potentiometer and the other end of wire 34 being connected to a conductor wire extending axially through the centre of core 32 and base 33 to form a further terminal 36. Thus if a potential difference is applied between terminals 35 and 36 a potential gradient will be established aixally along the length of the resistance member 31.

An annular cylinder 37 of insulating material, which is preferably of P.T.F.E., surrounds member 31 and is rotatable relative thereto by means of a screw head 38 provided at one end thereof. Member 37 is provided with an internal sleeve 39 of metal having an internal screw thread. A contact member 40, shown more clearly in FIG. 4, and having two integral arms 41 and 42 which embrace resistance member 31 lies in the screw thread. Electrical contact between contact member 40 and resistance wire 34 is maintained by a light leaf spring 45 secured to contact member 40 and bearing against the surface of core 31. Contact member 40 has a hole 43 through which there extends a fixed metal rod 44 which lies parallel to the axis of resistance member 31.

On rotation of member 37 by means of screw head 38 it will be seen that contact member 40 will be prevented from rotation by the support exerted by rod 44 and the reaction of the resistance member 31 against arm 41 or 42. Thus as member 37 is rotated contact member 40 progresses axially relative to the core. Rod 44 is extended to form an external terminal 46 and the potential of this external terminal can be varied between the potentials of terminals 35 and 36 by rotation of head 38. Alternatively electrical connection to contact mem ber 40 could be made by a wiping contact bearing against sleeve 39. A metal housing 47 surrounds rotatable member 37 and is secured to base 33.

As with the previous described embodiment the potentiometer cannot be over run at either end since excess rotation of member 37 will merely cause contact member 40 to jump the threads in which it lies without any damage being caused.

What I claim is:

1. A potentiometer comprising a resistance member of generally cylindrical shape, an annular rotatable mem ber surrounding the resistance member and defining an annular gap between said resistance member and said rotatable member, an internal screw thread provided on said rotatable member, a contact member which lies in said screw thread and which extends across said gap to register against said resistance member, and means for preventing rotation of said contact member about said resistance member whereby rotation of the rotatable member causes movement of the contact member axially of the resistance member, an electrical connection from said contact member to a fixed terminal, and at least one further terminal connected to the resistance member.

2. A potentiometer comprising a resistance member of generally cylindrical shape but having non-symmetrical portions extending axially thereof, an annular rotatable member surrounding said resistance member and having an internal screw thread, a contact member lying in said screw thread, said contact member having at least one integral contact finger registering against said non-symmetrical portion of said resistance member which prevents said contact member from rotating, whereby rotation of said rotatable member causes movement of said contact member axially of said resistance member, at least two fixed terminals, an electrical connection from one of said fixed terminals to said contact member and an electrical connection from at least one other terminal to said resistance member.

3. A potentiometer comprising a resistance member of generally cylindrical shape but having at least one fiattened portion extending axially thereof, an annular rotatable member surrounding said resistance member and having an internal screw thread, a contact member lying in said screw thread, said contact member having at least one integral contact finger registering against said flattened portion of said resistance member which prevents said contact member from rotating, whereby rotation of said rotatable member causes movement of said contact member axially of said resistance member, at least two fixed terminals, an electrical connection from one of said fixed terminals to said contact member and an electrical connection from at least one other terminal to said resistance member.

4. A potentiometer comprising a resistance member of generally cylindrical shape, an annular rotatable member surrounding said resistance member and having an internal screw thread, a contact member lying in said screw thread said contact member having integral arms at least partially embracing said resistance member and in contact therewith, a fixed rod extending parallel to the axis of said resistance member through said contact member rotation of said rotatable member causing movement of said contact member axially of said resistance member, at least two fixed terminals, an electrical connection from one of said fixed terminals to said contact member and an electrical connection from at least one other terminal to said resistance member.

5. The potentiometer as claimed in claim 4 in which said electrical connection from one of said fixed terminals to said contact member is taken through said fixed rod.

6. The potentiometer as claimed in claim 4 and including a light contact spring secured to said contact member and bearing against the surface of said resistance member.

7. A potentiometer comprising a resistance member of generally cylindrical shape, an annular cylindrical rotatable member surrounding said resistance member and having an internal screw thread, the axis of said resistance member extending parallel to and offset from the axis of said annular member, a contact member lying in said screw thread, said contact member having integral arms at least partially embracing said resistance member and in contact therewith, rotation of said rotatable member causing movement of said contact member axially of said resistance member, at least two fixed terminals, an electrical connection from one of said fixed terminals to said contact member and an electrical connection from at least one other terminal to said resistance member.

References Cited in the file of this patent UNITED STATES PATENTS 2,934,732 Schendel Apr. 26, 1960 

